1. Field of the Invention
This invention relates to the synthesis and purification of 3,3-dimethylbutyraldehyde via hydrolysis of 1,1-dichloro-3,3-dimethylbutane or 1-bromo-1-chloro-3,3-dimethylbutane with high purity.
2. Related Background Art
A method for synthesizing 3,3-dimethylbutyraldehyde via hydrolysis of 1,1-dichloro-3,3-dimethylbutane at 300.degree. C. with a 60% yield is reported by L. Schmerling J. Am. Chem. Soc., vol. 68, 1946, pp. 1650-1654. This reaction would generate hydrochloric acid but was carried out in a closed system by heating a mixture of water and 1,1-dichloro-3,3-dimethylbutane without addition of a base. It is well known that hydrochloric acid is very corrosive to typical commercial reactors, which are constructed of metal alloys, especially at high temperature and pressure. Such reaction conditions are highly undesirable because they may lead to structural failure of the reactors and may be very hazardous.
A method for synthesizing 3,3-dimethylbutyraldehyde via hydrolysis of 1,1-dichloro-3,3-dimethylbutane at 180.degree.-200.degree. C. is disclosed in Soviet Patent No. 721400. The method disclosed therein comprises heating 1,1-dichloro-3,3-dimethylbutane with water in the presence of catalytic amounts of magnesium oxide or triethylamine, at 180.degree.-200.degree. C. The yield is reported to be 88-90%.
However, repetition of this reported reaction was found to give a significant amount (30-40%) of cis and trans tert-butyl vinyl chloride and 43% of the starting material remained unreacted. This is highly undesirable because the boiling points of 3,3-dimethylbutyraldehyde and tert-butyl vinyl chloride are very close; hence, they can not be separated by distillation techniques.
Purification of aldehydes by their conversion into a solid aldehyde/bisulfite adduct has been described in the literature. "Purification of Laboratory Chemicals" (Pergamon Press, 1988), pages 60-61, is incorporated by reference herein as a general reference for this methodology. Typically, the crude aldehyde is stirred with aqueous sodium bisulfite or sodium bisulfite in a mixture of water and alcohol. The precipitates are isolated, washed with water and/or alcohol, and then converted into free aldehyde with a base or acid.
3,3-Dimethylbutyraldehyde is an intermediate that is useful in the preparation of the sweetener N-[N-(3,3-dimethylbutyl)-L-.alpha.-aspartyl]-L-phenylalanine disclosed in U.S. Pat. No. 5,480,668, U.S. Pat. No. 5,510,508 and U.S. Pat. No. 5,728,862. Thus, despite the techniques for the hydrolysis of 1,1-dichloro-3,3-dimethylbutane described in the prior art, it is clear that there is a need to economically produce 3,3-dimethylbutyraldehyde using more efficient methods than currently available.